Designer fuels from wastes - more power, less contrails
Really interesting opportunities are emerging from the progress we are making in sustainable aviation fuels. One is the scope for improving fuel quality, not only in performance but also in their environmental impact.
Opportunities for improvement
Because our process is different to processing fuel from oil, we use different type of equipment to generate the fuel from waste. The Fischer-Tropsch reactor allows for the more accurate calibration of fuels and therefore using this reactor allows us to create high grade, designer fuel.
Two steps – breakdown and rebuilding
Making replacement liquid fuels from waste materials involves two key steps. Firstly, the wastes get broken down into carbon monoxide and hydrogen, in a process known as gasification. Then secondly, these two gases are combined to form paraffins and other compounds closely related to those in the fossil-derived fuels. The Avioxx process aims to generate a stable and consistent supply of these two gases from a very variable supply of waste materials fed to the first stage. This is critical in enabling the second stage, the rebuilding of the fuel, to be managed and optimised, so yielding a highly consistent fuel product of the desired composition.
Better performance through tailoring the composition
Our work in this field has opened up the prospect of closely tailoring fuels to perform better, both in terms of delivering the power that aircraft need, and of eliminating effects which are environmentally damaging.
For example, it is well known that contrails have a bad environmental impact and are thought to develop from carbon particulates formed in the jet engines. Research into carbon formation in jet engines is well-established and has shown that it is dependent on the chemical composition (in terms of C:H ratio) and volatility. As one might expect, light, volatile paraffins are good and heavy aromatic compounds are bad. To illustrate this point, the tendency to deposit carbon is seven times higher for typical aromatic fuels than standard aviation kerosene, whilst light paraffins have only one tenth of the tendency.
The economic performance of fuels is a highly complex field that has been heavily researched over the years and involves not only calorific value but other properties. Nevertheless, there appears to be scope for further optimisation of the composition which we believe can be achieved through our process know-how and analytical techniques.
Reactor design and sophisticated control
The second stage of the Avioxx process involves the combination of carbon monoxide and hydrogen over a catalyst made of iron and cobalt, installed in tubes which are cooled on the outside. This is a very well-established process and is known to be tricky to control. The output is a waxy material with a wide composition. This product complexity is partly due to the varying temperatures across the reactor both radially and axially.
Our aim is therefore to both design and control this second stage of the process so as to minimise aromatic compound formation, and to maximise the lighter paraffins within the limits of the Jet 1A fuel specifications. By doing this we will narrow down the distribution of compounds produced to the ones which we want, rather than a mixture containing more of the heavy paraffins, aromatics and others than we would like.
Our reactor design experts and control analysts have already made good progress, building on the work that others have done in this field over the years. The age of designer-fuels is upon us and Avioxx is leading the way.